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  • General Chemistry  (11)
  • Polymer and Materials Science  (10)
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  • 1
    ISSN: 1434-1948
    Schlagwort(e): Silicon ; Silyl anions ; Lithium ; Silanes ; Polysilyl dianions ; α,ω-Dilithiooligosilanes ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: (Me3Si)3Si(Me2Si)2(Me3Si)2SiLi (1) and LiSi(Me3Si)2(Me2Si)2Si(Me3Si)2Li (2) were synthesized by the reaction of (Me3Si)3Si(Me2Si)2Si(Me3Si)3 in THF with one or two mol-equivalents, respectively, of MeLi. Both 1 and 2 were characterized spectroscopically and by trapping reactions, and 1 also by X-ray crystallography.
    Zusätzliches Material: 1 Ill.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 2
    Digitale Medien
    Digitale Medien
    Weinheim : Wiley-Blackwell
    Macromolecular Chemistry and Physics 197 (1996), S. 1349-1360 
    ISSN: 1022-1352
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: Model compounds for a series of polyesters in which 3,6,9, and 12-rotatable CH2—O and CH2—CH2 bonds separate rigid units have been studied using the efficiency of nonradiative singlet energy transfer from naphthalene to anthracene. The model compounds have the structure naph-CO—(OCH2CH2)m—OOC-anth with m of 1-4, where naph and anth denote 2-naphthyl and 9-anthranyl groups, respectively. This series of compounds covers a larger range of potential separation of the two chromophores than was possible in an earlier study, in which the flexible spacers consisted of 2-6 methylene units. The nonradiative singlet energy transfer has an efficiency that depends on the solvent viscosity and on m. The theoretical analysis employs a rotational isomeric state model for the conformations of these molecules. The Förster radius for transfer from naphthalene to anthracene in this system is 16 ± 2 Å, and is nearly independent of whether the spacers are constructed from oxyethylene or methylene units.
    Zusätzliches Material: 10 Ill.
    Materialart: Digitale Medien
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  • 3
    Digitale Medien
    Digitale Medien
    Weinheim : Wiley-Blackwell
    Macromolecular Chemistry and Physics 198 (1997), S. 3863-3869 
    ISSN: 1022-1352
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: Two poly(2-vinylpyridine)s fully quaternized with a ω-(4′-methoxy-4-biphenylyloxy)-alkyl group (alkyl chain of 9 and 11 carbon atoms) have been synthesized by the well known spontaneous polymerization of vinylpyridinium salts. When heated, these polymers (P2VPC9 and P2VPC11) show thermotropic liquid crystal properties. According to the X-ray diffraction data, the observed smectic mesophase in both polymers is of the type A (SA). Results are discussed in comparison with other molecular and polymeric pyridinium salts previously described. A molecular arrangement model for the P2VP derivatives is proposed.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 4
    ISSN: 0959-8103
    Schlagwort(e): anthracene ; fluorescence ; naphthalene ; non-radiative singlet energy transfer ; polyesters ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Steady state fluorescence has been used to study the efficiency of nonradiative single energy transfer for naphthalene → naphthalene and naphthalene → anthracene for polyesters and their bichromophoric model compounds. Polyesters containing only naphthalene groups were derived from 2,6-naphthalene dicarboxylic acid as the rigid unit, and two series of glycols, HO—(CH2)m—OH and HO—(CH2CH2O)n;—OH, where m=2-6 and n=1-4, as flexible spacers. Bichromophoric model compounds were derived from 2-naphthoic acid and the same glycols. In order to study the transfer for naphthalene → anthracene, a first attempt was made by studying bichromophoric model compounds D—(CH2)m—A, where D and A denote 2-naphthoate (donor) and 9-anthranoate (acceptor) groups, respectively. The fluorescence anisotropy measurements in a solid matrix of glassy poly(methyl methacrylate), for the compounds containing only naphthalene groups, and the simple excitation and emission spectra, for the compounds containing naphthalene and antharacene groups, clearly demonstrate the presence of non-radiative singlet-singlet energy transfer, the efficiency of which depends mainly on n (or n). A theoretical treatment using the rotational isomeric state model of the conformatin of these molecules has also been performed. The combination of the experiments and the theoretical analysis establishes that the Förster radii are 1.2 and 1.4 nm for the naphthalene → naphthalene transfer in the bichromophoric model compounds and polyesters, respectively, and 1.6 ± 0.2 nm for the naphthalene → anthracene transfer in the model compounds studied.
    Zusätzliches Material: 16 Ill.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 5
    ISSN: 0025-116X
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: The diester of itaconic acid with decyl and methyl groups was prepared and polymerized. The dilute solution behaviour of poly(methyl decyl itaconate) poly{1-(decyloxycarbonylmethyl)-1-(methoxycarbonyl)ethylene} (PMeDI) was studied in tetrahydrofuran and 1-butanol at 298 K, by light scattering, size-exclusion chromatography, and viscometric measurements. The empirical Kuhn-Mark-Houwink-Sakurada relationships were established. The molecular parameters were calculated using one theory of the excluded volume.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 6
    ISSN: 1434-193X
    Schlagwort(e): Fluorine ; Sulfoxides ; Nucleotide analogues ; Asymmetric synthesis ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: D- and L-(diethoxyphosphoryl)difluoromethyl nucleoside analogues 10 have been synthesized using the building block approach, starting from chiral fluorinated molecules. The key steps of the synthetic sequence were condensation of 2-methyl-5-(4-methylphenylsulfinyl)pent-2-ene (1) and ethyl 2-(diethoxyphosphoryl)-2,2-difluoroacetate (2), reduction of the thus formed ketones 3 to alcohols 4, reductive removal of the sulfur moiety to give hydroxy phosphonates 6, and oxidative cyclization to give furanose derivatives 8.
    Zusätzliches Material: 3 Tab.
    Materialart: Digitale Medien
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  • 7
    ISSN: 1434-193X
    Schlagwort(e): Co-conformation ; Molecular recognition ; Planar chirality ; Rotaxanes ; Template-directed synthesis ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: -The template-directed syntheses of three [2]rotaxanes possessing either chiral centers or elements of planar chirality, in one of their two mechanically interlocked components, have been realized and their solid-state structures have been analyzed by X-ray crystallography. In one instance, an enantiomerically pure dumbbell-shaped component incorporating a 1,5-dioxynaphthalene recognition site and two (1R,2S,5R)-menthyl stoppers was employed to template the formation of the achiral tetracationic cyclophane, cyclobis(paraquat-p-phenylene). The resulting enantiomerically pure [2]rotaxane was isolated in a yield of 55%. In the other two instances, an achiral 1,5-dioxynaphthalene-based dumbbell-shaped component was employed to template the formation of bipyridinium-based cyclophanes possessing either one or two elements of planar chirality. The resulting [2]rotaxane, possessing one element of planar chirality, was isolated as a racemate in a yield of 24%. The related [2]rotaxane, possessing two elements of planar chirality, was isolated as a mixture of a meso form and an enantiomeric pair in an overall yield of 28%. The 1H-NMR-spectroscopic analysis of this mixture revealed a diastereoisomeric ratio of 4:1. A degenerate co-conformational change was identified by variable-temperature 1H-NMR spectroscopy in all [2]rotaxanes. The symmetry loss arising from the introduction of one or two elements of planar chirality enabled the elucidation of the mechanism of this dynamic process in two instances.
    Zusätzliches Material: 12 Ill.
    Materialart: Digitale Medien
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  • 8
    ISSN: 1434-193X
    Schlagwort(e): Fluorine ; Lactones ; Annulation ; Ketene ; Sulfoxides ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: -Enantiomerically pure α,α-dichloro β-fluoroalkyl γ-p-tolylthio γ-butyrolactones trans-6a-c have been obtained with excellent stereocontrol (〉 98:2) and enantiomeric purity (〉 98:2) by sulfoxide-directed lactonization (Marino's annu-lation reaction) of β-fluoroalkyl vinyl sulfoxides (R)-(E)-5a-c with dichloroketene. Highly chemoselective dechlorination and desulfurization reactions performed on trans-6c efficiently provided the β-chlorodifluoromethyl γ-butyrolactone (S)-8c, the absolute stereochemistry of which was determined by X-ray diffraction analysis of its γ-p-tolylthio precursor (2R,3S)-7c.
    Zusätzliches Material: 1 Ill.
    Materialart: Digitale Medien
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  • 9
    ISSN: 1434-193X
    Schlagwort(e): β-Iminosulfoxides ; Quaternary stereocentre ; Pictet-Spengler reaction ; Alkaloids ; Fluorine ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Enantiomerically pure 1-trifluoromethyl-tetrahydroisoquinoline alkaloid analogues, in which C-1 is a quaternary stereogenic centre, have been synthesized by stereoselective intramolecular Pictet-Spengler reaction of the N-arylethyl γ-trifluoro-β-iminosulfoxide (R)-3, and subsequent elaborations of the sulfinyl auxiliary. The absolute stereochemistry of the stereogenic centre was determined by X-ray diffraction on the α-phenylpropionic ester (1R,2′S)-10.
    Materialart: Digitale Medien
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  • 10
    Digitale Medien
    Digitale Medien
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 2565-2571 
    ISSN: 1434-193X
    Schlagwort(e): Molecular recognition ; Rotaxanes ; Self-assembly ; Template-directed synthesis ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Three dumbbell-shaped compounds incorporating terminal triisopropylsilyl stoppers, connected to a central 1,5-dioxynaphthalene recognition site by [-CH2CH2O-]n spacers (n = 1-3), have been synthesized. These compounds have been employed as templates for the synthesis of [2]rotaxanes incorporating cyclobis(paraquat-p-phenylene) as the ring component. It was found that the length of the polyether chains of the templates influences the efficiencies of the template-directed syntheses. Rotaxane formation occurs only if n 〉 1 and, when n = 3 the corresponding [2]rotaxane can be isolated in a yield as high as 72 %. This remarkable yield is the highest ever obtained for the template-directed syntheses of [2]rotaxanes incorporating donor/acceptor interactions.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
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